<p>Methylmercury is a bioaccumulative neurotoxin that severely endangers human health. Humans are exposed to methylmercury through consumption of contaminated aquatic fish. To date, effective strategies for preventing and remediating methylmercury contamination have remained elusive, mainly due to the lack of knowledge in regard to how methylmercury is generated and degraded in the aquatic environment. The goal of this dissertation was to study the mechanisms of two transformation processes that govern the fate of methylmercury in natural settings: microbial mercury methylation and methylmercury photodegradation. The role of mercury speciation (influenced by environmental conditions) in determining the reactivity of mercury in these biological and photochemical reactions was the focus of this research.</p><p>Methylmercury production in the aquatic environment is primarily mediated by anaerobic bacteria in surface sediments, particularly sulfate reducing bacteria (SRB). The efficiency of this process is dependent on the activity of the methylating bacteria and the availability of inorganic divalent mercury (Hg(II)). In sediment pore waters, Hg(II) associates with sulfides and dissolved organic matter (DOM) to form a continuum of chemical species that include dissolved molecules, polynuclear clusters, amorphous nanoparticles and after long term aging, bulk-scale crystalline particles. The methylation potential of these mercury species were examined using both pure cultures of SRB and sediment slurry microcosms. The results of these experiments indicated that the activity of SRB was largely determined by the supply of sulfate and labile carbon, which significantly influenced the net methylmercury production in sediment slurries. The availability of mercury for methylation decreased during aging. Dissolved Hg-sulfide (added as Hg(NO3)2 and Na2S) resulted in the highest methylmercury production. Although the methylation potential of humic-coated HgS nanoparticles decreased with an increase in the age of nanoparticle stock solutions, nano-HgS was substantially more available for microbial methylation relative to microparticulate HgS, possibly due to the smaller size, larger specific surface area and more disordered structure of the nanoparticles. Moreover, the methylation of mercury derived from nanoparticles cannot be explained by equilibrium speciation of mercury in the aqueous phase (<0.2 <em>f</em>Ým, the currently-accepted approach for assessing mercury bioavailability for methylation). Instead, the methylation potential of mercury sulfides appeared to correlate with the extent of dissolution and their reactivity in thiol ligand exchange. Additionally, partitioning of mercury to a diverse group of bulk-scale mineral particles and colloids (especially FeS) may be an important process controlling the mercury speciation and subsequent methylmercury production in natural sediments.</p><p>In surface waters, sunlight degradation is believed to be the predominant pathway for the decomposition of methylmercury. The mechanism of this process was investigated in a series of photodegradation experiments under natural sunlight and UV-A radiation, and in the presence of DOM and selective quenchers for photo-generated reactive intermediates. The results suggested that singlet oxygen generated from photosensitization of DOM drove the photodecomposition of methylmercury. The rate of methylmercury degradation depended on the type of methylmercury (CH3Hg+) binding ligand present in the water. CH3Hg -thiol (e.g., glutathione, mercaptoacetate, DOM) complexes were significantly more reactive in photodegradation compared to other methylmercury complexes (CH3HgCl or CH3HgOH), which may be because thiol-binding can effectively decrease the activation energy and thus enhance the reactivity of methylmercury molecules toward the Hg-C bond breaking process. These findings challenge the long-accepted view that water chemistry characteristics do not affect the kinetics of methylmercury sunlight degradation, and help explain recent field observation that methylmercury photodegradation occurred rapidly in freshwater lakes (where CH3Hg-DOM dominate methylmercury speciation) but relatively slowly in sea water (where CH3Hg-Cl control methylmercury speciation).</p><p>Overall, this dissertation has demonstrated that chemical speciation of inorganic mercury and methylmercury determines their availability for microbial methylation and sunlight degradation, respectively. The abundance of these available mercury species is influenced by a variety of environmental parameters (e.g., DOM). This dissertation work contributes mechanistic knowledge toward understanding the occurrence of methylmercury in the aquatic environment. This information will ultimately help construct quantitative models for accurately predicting and assessing the risks of mercury contamination.</p> / Dissertation

This dissertation examines the role of donor-funded international projects to reduce mercury pollution from artisanal and small-scale gold mining (ASM). ASM is the second largest source of anthropogenic global mercury pollution, accounting for roughly 1000tonnes of atmospheric emissions and releases to the environment per annum. The artisanal mining economy involves 10-15 million people across the developing world, and supports 80-100 million people directly and indirectly. In 2003 the Governing Council of the United Nations Environment Program reached consensus that there is sufficient scientific evidence to trigger an international response to global mercury pollution, including the pollution generated by ASM. Yet thus far most international interventions have concentrated on environmental monitoring and assessment, while virtually no efforts have focused on implementing solutions. The aim of this dissertation is to move global mercury policy for ASM past its emphasis on assessments. It does this by developing a philosophical and strategic policy framework to guide future interventions by international institutions. A brief history of global mercury policy is provided, illustrating how ASM has been neglected and examining divisions between ecocentric and technocentric theories of environmental intervention. The relationship between ASM and poverty is examined, reaching the conclusion that because artisanal gold mining is a form of upward mobility for the world's extreme poor, the idea of reducing mercury pollution by redirecting miners into alternative livelihoods is unrealistic; indeed gold itself is the alternative livelihood. Using case studies collected in the field, the issue of conflict over property rights between artisanal miners and large-scale mining companies is explored, and a risk mitigation framework presented to assist companies to coexist with artisanal miners. Finally, a new approach to international intervention is proposed based on three interdependent principles of formalization, capitalization, and education. A plan is developed for directing more expertise and financial resources to the field, and more effectively meeting the needs of miners. Specific recommendations include a rapid assessment methodology to select project sites, and improving operational linkages among public and private institutions.

Snow and ice can significantly affect the environmental fate of contaminants. This thesis presents a laboratory technique for measuring mercury in metamorphosing snow, and a computer model for organic contaminants in a seasonally ice covered ocean. The laboratory method to study the fate of mercury in snow was developed using laboratory-made snow of controlled composition made in a cold room, aged and melted, with mercury quantified in air, snow, and dissolved and particulate fractions of the melt water. It was found that the method gave a mass balance for mercury, and can be used to look at mercury fate in snow representative of different environments. The fugacity based fate and transport model for organic contaminants in a seasonally ice-covered ocean was parameterized to Barrow Strait, and tested against environmentally derived net air to sea water fluxes. It was found that the model could reproduce these environmental data.

The effects of different types and amounts of dissolved organic matter (DOM) on the isotope fractionation of Hg isotopes during aqueous photo-reduction of monomethylmercury (MMHg) were investigated to assess whether mass-independent fractionation (MIF) signatures can be used to track photo-degradation of MMHg in natural waters. From experiments conducted with different amounts of reduced organic sulfur (Sred-DOM), it appears that MIF during photo-reduction may be dependent on whether MMHg is dominantly bound to Sred-DOM. Similar fractionation factors were observed for experiments where Sred-DOM was in far excess of MMHg, while significantly lower fractionation factors were observed with lower Sred-DOM. We also characterized the signature of MIF (i.e. Δ199Hg/Δ201Hg) during MMHg photo-degradation to assess if it was similar in different matrices. The experimental Δ199Hg/Δ201Hg was very similar for different matrices. However, the experimental slope is slightly but statistically different than the slope observed in freshwater fish, which preserve MMHg in nature.

With the prospect of future construction on the Skutskär Pulp Mill property, Stora Enso Fine Paper has initiated an investigation of soil contaminants and a risk assessment of these contaminants. A soil and groundwater investigation has therefore been conducted on an open area of about 16 000 square meters, situated between the current wood room and digester house. To be able to integrate this study into an investigation for the whole industrial property, the study has been carried out as a phase 2 study according to the Swedish Environmental Protection Agency’s Methods of Inventories of Contaminated sites (MIFO). The site investigation has involved soil and groundwater sampling, together with the analysis of heavy metals and organic contaminants. The degree of hazard posed by the contaminants, the level of contamination, the potential for migration of the contaminants, as well as the degree to which protection of human health and the environment is required in the area, have been weighed together for an overall risk assessment of the area with regard to human health and the environment. The investigated area was built up by filling in the coastal waters. The fill material consists mainly of sand that becomes finer below the groundwater surface at the depth of about 2.3 m. Above the groundwater surface pyrite cinders was encountered. Underneath the cinders, lime sludge, bark and wood fiber were found at different depths. The deepest layer encountered consists of moraine. The results showed that most of the heavy metals in the soil originate from the pyrite cinders. The level of contamination was assessed as very high for Zn, Pb, Cu, Cd and Hg. In the groundwater, the level of contamination was assessed as high for Al and moderate for Pb and Cr. The level of organic contaminants was in general low. Heavy oils were encountered in shallow soil layers. Mercury was analysed due to risk of migration from an earlier factory that produced chlorine alkali. The metal was encountered in both the shallow and the deeper layers of soil. Only three of 56 soil samples exceeded the Swedish Environmental Protection Agency’s guideline value for less sensitive land use of 7 mg Hg/kg dry weight. The investigation indicates that the metals still are bound to the pyrite cinders and that most of the leachable parts were mobilized during the years when the ground was not covered with asphalt. Most of the contaminant migration is assumed to take place through groundwater advection. The groundwater flows in the direction of the dock and was calculated to about 3 m3 per day. The gradient in the area is about 0.5 %. The average linear groundwater velocity was computed to about 5 m per year. The transport of the pollutants might be slower due to adsorption and precipitation. Groundwater sampling indicates that the transport to the dock is up to 100 g Zn, 10 g Cr, 8 g Pb and 0.02 g Hg per year. The site was assigned to risk class 3, i.e. moderate risk regarding human health and environment and relatively low urgency concerning additional investigations. / Inför framtida ombyggnationer inom industrifastigheten vill Skutskärs Bruk, Stora Enso, kartlägga markföroreningar och utvärdera vilken spridningsrisk de utgör. En undersökning av mark- och grundvattenförhållanden har därför utförts på en ca 16 000 m2 stor yta, belägen mellan dagens renseri och kokeri. Undersökningen har utförts enligt Naturvårdsverkets Metodik för Inventering av Förorenade Områden (MIFO) för att i framtiden kunna integreras i en fas 2- undersökning för hela fastigheten. Arbetet har inneburit provtagning av mark- och grundvatten som analyserats med avseende på tungmetaller och organiska föroreningar. Föroreningarnas farlighet, föroreningsnivån, spridningsförutsättningarna samt objektets känslighet och skyddsvärde har vägts samman för att bedöma områdets risk för människors hälsa och miljö. Området utgörs av utfylld havsbotten. Massorna består främst av sand som blir siltigare under grundvattenytan på ca 2,3 m djup under markytan. Ovan grundvattenytan påträffades kisaska. Därefter hittades mesa, bark och träfiber på varierande djup. Fyllningen underlagras av morän. Resultatet visade att huvuddelen av tungmetallerna i marken härstammade från kisaskan. Föroreningsnivån bedömdes som mycket stor för Zn, Pb, Cu, Cd och Hg. I grundvattnet bedömdes föroreningsnivån som stor för Al och måttlig för Pb och Cr. Halten organiska föroreningar var generellt sett låg. Tyngre oljor påträffades i ytliga marklager. Kvicksilver har analyserats eftersom risk för spridning från en före detta kloralkalifabrik uppströms området förelåg. Ämnet påträffades både i ytnära marklager och på större djup. Endast tre av 56 markprover översteg Naturvårdsverkets gränsvärde för mindre känslig markanvändning på 7 mg/kg TS. Undersökningen tyder på att metallerna fortfarande är bundna till kisaskan och att stora delar av den lakbara delen transporterades bort under de år som ytan var oasfalterad. Huvuddelen av föroreningstransporten antas ske genom advektion. Grundvattnet flödar i riktning mot hamnbassängen och beräknas uppgå till ca 3 m3/dygn. Områdets gradient är ca 0,5 %. Vattenpartiklarnas hastighet beräknades till ca 5 m/år. Föroreningstransporten kan vara lägre på grund av adsorption och utfällning. Grundvattenprovtagningen tyder på att den årliga transporten till hamnbassängen skulle kunna uppgå till 100 g Zn, 10 g Cr, 8 g Pb och 0,02 g Hg. Objektet bedömdes tillhöra riskklass 3, det vill säga måttlig risk för människa och miljö samt relativt låg angelägenhet för vidare undersökningar.

Snow and ice can significantly affect the environmental fate of contaminants. This thesis presents a laboratory technique for measuring mercury in metamorphosing snow, and a computer model for organic contaminants in a seasonally ice covered ocean. The laboratory method to study the fate of mercury in snow was developed using laboratory-made snow of controlled composition made in a cold room, aged and melted, with mercury quantified in air, snow, and dissolved and particulate fractions of the melt water. It was found that the method gave a mass balance for mercury, and can be used to look at mercury fate in snow representative of different environments. The fugacity based fate and transport model for organic contaminants in a seasonally ice-covered ocean was parameterized to Barrow Strait, and tested against environmentally derived net air to sea water fluxes. It was found that the model could reproduce these environmental data.

The effects of different types and amounts of dissolved organic matter (DOM) on the isotope fractionation of Hg isotopes during aqueous photo-reduction of monomethylmercury (MMHg) were investigated to assess whether mass-independent fractionation (MIF) signatures can be used to track photo-degradation of MMHg in natural waters. From experiments conducted with different amounts of reduced organic sulfur (Sred-DOM), it appears that MIF during photo-reduction may be dependent on whether MMHg is dominantly bound to Sred-DOM. Similar fractionation factors were observed for experiments where Sred-DOM was in far excess of MMHg, while significantly lower fractionation factors were observed with lower Sred-DOM. We also characterized the signature of MIF (i.e. Δ199Hg/Δ201Hg) during MMHg photo-degradation to assess if it was similar in different matrices. The experimental Δ199Hg/Δ201Hg was very similar for different matrices. However, the experimental slope is slightly but statistically different than the slope observed in freshwater fish, which preserve MMHg in nature.

Recent research has shown that the Arctic may be a sink for mercury, however, the fate of this deposited mercury in the environment is not known. The objective of this project was to determine the factors affecting methyl mercury (MeHg) production in Arctic organic soil on the Truelove Lowlands, Devon Island, Canada. In the field we observed a steady decrease in MeHg over time, with MeHg concentration at many sampling locations declining below detection limits. This decrease did not correlate to any chemical or biophysical parameter measured. During the study the Lowlands appeared to be mildly reducing with dissolved Fe(II) being present in the porewater, however, no correlation was observed between MeHg production and the variables measured. The dissolved organic matter concentration of the porewater was quite high, the pH was circumneutral and it would seem that in the absence of more highly reducing conditions that mercury would be unavailable for methylation.<p> It seems likely under field conditions MeHg was much more bioavailable then inorganic mercury. This would lead to a higher rate of demethylation then methylation and a net decrease in MeHg. Little research has been done on demethylation and the effect of environmental conditions on demethylation, especially in arctic environments. However, it is possible that the rate of demethylation was not affected by changes in temperature or any other parameter measured over the course of the field study. <p> Laboratory microcosm studies using saturated soil from the organic horizons demonstrated little potential for unspiked organic soil to produce significant amounts of MeHg. The spiked treatment, however, had an eight fold increase in MeHg concentration and the sterile treatment showed no change in MeHg concentration over 40 days of freeze (-5 0C) and 59 days of thaw (4 oC). <p> Our data suggests that a combination of atmospheric and in-situ processes maintain a cycle of MeHg production (spring) and loss (summer) in arctic soils. It would seem that Arctic wetland soils are not a significant source of MeHg to the Arctic ecosystem and that snowmelt is the dominant source.

Although some physiological effects of toxic metal poisoning have been known for centuries, the specific chemical interactions between biological molecules and mercury(I), mercury(II) or lead(II) are not well understood. To date, only thirteen crystal structures of inorganic mercury-amino acid complexes and six crystal structures of lead-amino acid complexes have been reported with varying degrees of characterization. In order to improve our understanding of the coordination chemistry of mercury and lead in biological environments, a systematic method for the isolation of inorganic metal-amino acid complexes from acidic aqueous solutions has been developed. With this method we have prepared five new lead-amino acid complexes (with L-valine, L-isoleucine, L-phenylalanine, and L-arginine) and four new mercury-amino acid complexes (with L-alanine, D-alanine, L-proline, and N-methyl-L-alanine). These metal-amino acid complexes have been comprehensively characterized in the solid state, solution state and gas phase. The development of this isolation technique in conjunction with the exploration of a number of characterization techniques for studying metal-amino acid interactions greatly enhances the known methods by which metal-biological molecule systems are studied.

Kvicksilverutsläppen har på senare år minskat i omfattning men utsläpp sker fortfarande och det finns ett stort lager i naturen. Oorganiskt kvicksilver är relativt ofarligt för levande organismer, men i akvatiska miljöer kan sulfatreducerande bakterier under syrefria förhållanden omvandla oorganiskt kvicksilver till den betydligt mer skadliga formen metylkvicksilver, meHg, som även är mer biotillgängligt än oorganiskt kvicksilver. Kvicksilver biomagnifieras uppåt i trofinivåerna, från att vara lägst halter i plankton och bottenfauna till att vara högst halter i rovfiskar. Kvicksilver ackumuleras även i fiskars muskelvävnad vilket innebär att yngre fiskar har lägre Hg-halter än gamla och stora individer. På grund av detta finns kostråd framtagna av Livsmedelsverket. Saluförd abborre, liksom ett flertal andra fiskarter, får inneha maximalt 0,5 mg Hg/kg fiskmuskel (färskvikt) och för gädda är gränsen satt till 1 mg Hg/kg fiskmuskel (färskvikt). Organiskt kvicksilver kan påverka foster negativt, och därför bör kvinnor i fertil ålder i största möjliga mån undvika kvicksilverrik fisk.   Examensarbetet syftar till att belysa kvicksilversituationen i Stockholms skärgård för stationär kustfisk. Information har samlats in dels genom en litteraturstudie och dels genom fältundersökningar utförda av IVL Svenska Miljöinstitutet. Genom statistisk analys och stegvis multipel regression visades att kvicksilverhalten i sediment, vattnets klorofyllhalt och områdets vattenvolym bidrog med förklaringsgrad till halten Hg i fisk. Utifrån de mest signifikanta förklarande variablerna togs en statistisk modell fram i syfte att kunna prediktera teoretiska kvicksilverhalter i fisk. Olika modellkombinationer testades och utgående från en modellvalidering valdes den bästa modellen ut. Dess förklaringsgrad är 81 % där kvicksilverhalten i sediment är modellens enda variabel.   Kvicksilversituationen i Stockholms skärgårds kustområden visades grafiskt med hjälp av interpolerade GIS-kartor. Samma områdesavgränsningar användes som i SMHI:s havsområderegister. Det visades att situationen över lag är relativt god, med undantag för de centrala delarna av Stockholm och på så vis kan Stockholm ses som en förorenande punktkälla. / Mercury emissions have been reduced in recent years but the discharges still exist and there exist a great mercury stock out in the nature. Inorganic mercury is relatively harmless for living organisms but during shortage of oxygen, sulphur reducing bacteria can transform inorganic mercury into the considerable more toxic substance methyl mercury, meHg, that are more bio available than inorganic mercury. Mercury biomagnify upwards the trophic levels, where the lowest content exists in algae and sediment living fauna and the highest content exist in predator fishes. Mercury also accumulates in fishes muscle tissue, meaning that young fishes have lower mercury content than old and big individuals. Food advices from the Swedish food agency exist because of this. Perch offered for sale are allowed to have a content of maximum 0.5 mg Hg/kg fish muscle (wet weight) and for pike the upper boundary content is 1 mg Hg/kg fish muscle (wet weight). Inorganic mercury can affect foetus negatively, and therefore women in fertile age should avoid fish with high mercury content for as long as possible.   The aim of this exam work is to illustrate the mercury situation in the archipelago of Stockholm regarding stationary coast fish. Information was collected through a literature study and by field examines done by IVL Swedish Environmental Research Institute Ltd. Through statistical analyses and stepwise multiple regression it was shown that the mercury content in sediment, chlorophyll and the water volume of the area contributed by statistical explanation to the mercury concentration in fish. On the basis of the most significant variables a statistical model was created, with the purpose of predicting theoretical mercury contents in fish. Different model combinations were tested and by a model validation the best model were chosen. Its statistical explanation is 81 % were the mercury content in the sediment is the only input variable to the model.   The mercury situation in the Stockholm archipelago was presented graphically by interpolated maps created with GIS. The same area boundary as SMHI’s maritime registry was used. It was shown that the situation in general is relatively good, with the exception of the central parts of Stockholm. Because of this Stockholm can be seen as a polluting point source.